RIM vs Fiberglass

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RIM offers

Lower Unit Costs

Less Environmental Harm

than Fiberglass
While fiberglass can be used to produce very large, structural parts, RIM can offer the same advantages with a lower unit cost.

Design Features

Traditional fiberglass molding is a slow, manual, and labor intensive process, and issues of conformity and accuracy can often arise in these parts. The RIM process can produce more uniform parts with features molded into the interior. While fiberglass is the best option for prototyping very large parts, it is possible to mold fibers or other materials into a RIM part to achieve the strength and weight advantage of fiberglass.


While both processes provide a solution for encapsulating metal, only RIM urethane is appropriate to use when the encapsulation of PCBs and other electronics is necessary.

Finish & Surfacing

Fiberglass parts have a high quality finish, but RIM parts take paint, silk screening and texturing much better for improved cosmetics.


Fiberglass is mostly used to make small quantities of prototype parts. RIM is more cost-effective for actual production of low to medium volumes (25-500 parts/month) compared to fiberglass. Neither process is the appropriate for higher production volumes.

Lead Times

Exothermic uses in-house machining centers to drastically reduce lead time and create production molds within 2 to 4 weeks; this timing is typically faster than a fiberglass mold can be created.

Tooling Costs

Both RIM and fiberglass tools require a low up-front cost, and both types of tools allow for cost-effective modification if market feedback shows that features need to be changed.

Other Design Benefits

Fiberglass production emits large amounts of hazardous styrenes. RIM is much more environmentally safe compared to fiberglass.

Though these are some of the main considerations to account for when deciding on a production process, there are many issues to balance when determining the most effective option. Let Exothermic help you uncover the opportunities for success and guide your design concept to meet those process needs.

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Industrial Designers

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